Aircraft: A321
Phase of flight: Parked
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Ground Event / Encounter Other / Unknown

At approximately XA:30 hours; just moments prior to boarding; I smelled a very strong; musty; wet dog like odor inside the cabin. As I walked back towards the AFT galley (at approximately mid-cabin); the odor became much stronger. I immediately called out to the lead F/A and asked her to come back to observe what I was smelling. [Lead F/A] stated she could also smell the odor. Accordingly; I immediately made my way to the cockpit. The odor became so strong that my throat started to burn; and I began coughing. I told the Captain that we were being fumed and that I was going to notify the boarding agent to immediately stop boarding in order to prevent further issues (i.e. passenger exposure.) The Captain stated that he was notifying maintenance and agreed to hold boarding. I left the aircraft (no passengers were onboard). While making my way up the jet bridge to notify the agent; customers were beginning to walk down the jet bridge since boarding had commenced. I was able to stop the passengers and advised them to stop; turn around and go back into the terminal since we were having maintenance come to the aircraft. I did not advise them why. I entered into the terminal and advised the agent in a discreet manner to stop boarding as we were experiencing an aircraft fume event. I then returned to the aircraft briefly to advise the Captain that the agent was notified. The crew exited the aircraft and we remained in the jet bridge area for a few moments until maintenance arrived. We collected our belongings and exited the jet bridge into the terminal to gain better air quality. I continued to experience a burning throat and my cough continued. At that time; it was prudent to seek medical attention; therefore; I contacted Medical to seek advisement. I was given a clinic appointment at [medical name] and was seen by a doctor accordingly.Improper aircraft maintenance was the cause.Recommendations - Contacting numerous departments; is too much following an incident like this. One call should automatically provide the needed support; guidance and direction that we require during events like this. Because this is my 3rd fume event; I was able to more quickly identify the inherent risks; take appropriate action to limit passenger exposure; and limit extended exposure; however; it was still medically concerning and we should have less calls to make following these dangerous occurrences. During the preflight the ground air was not sufficient to cool the aircraft. I had the ground crew turn off the ground air and the CA started the APU. After APU start; the CA started the APU BLEED. Almost immediately the CA and I smelled something strange. It did not smell terrible right away but it was cause for investigation. No passengers were on board yet. A FA came up to the flight deck saying he noticed a smell. At the point I radioed maintenance about the problem and we all exited the aircraft. A few minutes later the maintenance staff said they could smell the problem in the jetway. The whole crew then started the Fume Event process. We were all checked out at the on airport [company name] clinic. Reporter stated the cause was Aircraft XXX [which] is a known Fume Event multiple offender. I remember from my walk around that the belly of the aircraft had a high amount of oil streaks. When was this last belly washed? Airbus knows this is a problem and does not take it seriously. Reporter suggested company take known Fume Event aircraft out of service. Use them for parts; excluding the APU. Put filters like [other air carriers] has to protect crews and passengers. Implement bad air detection systems. A321 Flight Attendant reported a fume event during pre-flight that was reported to Captain who stopped boarding and referred aircraft to Maintenance.